Although experimental and clinical evidence as to the effects of castration, as well as numerous experimental transplantation studies, conclusively prove that the testes possess one or more endocrine functions, nevertheless the biochemical evidence for the extraction of a postulated hormone from testis tissue was not definitely established until recently. To be sure, numerous claims have been made from time to time, only to be unconfirmed later.
Brown-Séquard1 is credited with the preparation of the first extract. He prepared crude water extracts from dog and guinea-pig testes and claimed most remarkable effects from the subcutaneous administration of them on himself. He felt much improved in general, with greater capacity for physical and mental work and less need for laxatives. The general impression was that the subcutaneous injection of the product would prove beneficial in the treatment of the aged and of persons with neurasthenia. Later the product was improved2
KOCH FC. THE EXTRACTION, DISTRIBUTION AND ACTION OF TESTICULAR HORMONES. JAMA. 1931;96(12):937-939. doi:10.1001/jama.1931.02720380025008